Coreless Induction Furnace
The principle of induction melting is that a high voltage electrical source from a primary coil induces a low voltage, high current in the metal or secondary coil. Induction heating is simply a method of transferring heat energy.
Principles of Coreless Induction Furnace are:
The principle of Coreless induction Furnace heating is based on the following two laws:
1. Electromagnetic induction
2. The joule effect
Electromagnetic induction transfers energy to the material to be heated. In a variable magnetic field any electrically conductive material is a place with which induces electrical currents, called eddy currents, eventually contributing to Joule heating.
The joule effect
Joule heating is however known as ohmic heating or resistive heating, which is the procedure used to release heat through a conductor by transmission of electric current.
The amount of heat generated is proportional to the square of the current times the wire’s electrical resistance.
Types of Induction Furnace:
The induction furnace seems to be an electric furnace wherein the heat is supplied with metal induction heating. Induction Furnace can be used to smelt iron and steel, zinc, aluminium and desirable metal, from less than one kg to a hundred metric tonnes.
The electrical induction furnace is nonetheless a melting furnace which is used for melting metal by electric currents. The induction furnace is suitable for melting and alloying a large range of metals with minimal melt losses, but little metal refinement would be feasible.
These Induction Furnace can be classified into two categories. They are:
- Core type Induction Furnace or Low frequency Induction Furnace
- Direct core type
- Indirect core type
- Vertical Core type
- Coreless type Induction Furnace or High frequency Induction Furnace
High frequency Induction Furnace
The high frequency induction furnaces use the heat produced by eddy currents generated by a high frequency alternating field. The inductor is usually made of copper in order to limit the electric losses. Nevertheless, the inductor is in almost all cases internally water-cooled. The furnace consists of a crucible made of a suitable refractory material surrounded by a water cooled copper coil. In this furnace type, the charge is melted by heat generated from an electric arc. The coil carries the high frequency current of 500 to 2000 Hz.
The alternating magnetic field produced by the high frequency current induces powerful eddy currents in the charge resulting in very fast heating. Various configurations are available, with two or three electrodes high melting capacity (25 to 50 tons/hr) and they are used primarily for casting steel.
These currents also provide certain amount of agitation to the melting charge resulting in efficient mixing. Molten metal can be poured by tilting the furnace.
Coreless induction furnaces power supply system
Power is derived from the ordinary supply grid for coreless induction furnace, and its frequency is transformed by oscillators to a higher value. These oscillators can produce the order of megahertz with very high frequency.
A transformer amplifies the AC supply and then rectifies while using a bridge rectifier circuit. The rectification voltage shall be added to the oscillator and the high frequency output is supplied by a power transformer to the load to be heated.
Cupola Furnace vs Coreless Induction Furnace
In particular for melting of high melting point alloys, the Coreless Induction Furnace effectively replenished the cupola Oven. In general, the coreless induction furnace fuses all kinds of steels and iron and even non-ferrous alloys. The furnaces have high control over temperature and chemistry, whilst the induction and frequency control circulation of the melting current and are suitable for re-melting and alloying.
Advantages of Coreless Induction Furnace:
· Induction furnace does not need electrodes like electric arc furnace.
· Better control of temperature
· Better control of composition of the melt
Disadvantages of Coreless Induction Furnace:
· An induction installation usually implies a big investment that must be considered and compared to alternative heating techniques.
· Induction heating is preferably used for heating relatively simple shapes.
Materials to be casted in Coreless Induction Furnace:
· Steel alloys